Semiconductors are widely used in integrated circuits for electronic devices such as computers and televisions. These integrated circuits typically combine many transistors on a single crystal silicon chip to perform complex functions and store data. Semiconductor and electronics manufacturers, as well as end users, desire integrated circuits that can accomplish more functions in less time in a smaller package while consuming less power. Without limiting the scope of the invention, its background is described in connection with current methods of forming electrical connections to high-dielectric-constant materials used in integrated circuits, as an example.
The increasing density of integrated circuits (e.g., DRAMs) is increasing the need for materials with high-dielectric-constants to be used in electrical devices such as capacitors. Generally, capacitance is directly related to the surface area of the electrode in contact with the capacitor dielectric, but is not significantly affected by the electrode volume. The current method generally utilized to achieve higher capacitance per unit area is to increase the surface area/unit area by increasing the topography, such as in trench and stack capacitors using SiO.sub.2 or SiO.sub.2 /Si.sub.3 N.sub.4 as the dielectric. This approach becomes very difficult in terms of manufacturability, however, for devices such as the 256 Mbit and 1 Gbit DRAMs.
An alternative approach is to use a high permittivity dielectric material. Many perovskite. ferroelectric, or high-dielectric-constant (HDC) materials such as (Ba,Sr)TiO.sub.3 (BST) usually have much larger capacitance densities than standard SiO.sub.2 -Si.sub.3 N.sub.4 -SiO.sub.2 capacitors. Various metals and metallic compounds, and typically noble metals such as Pt and conductive oxides such as RuO.sub.2, have been proposed as the electrodes for these HDC materials. To be useful in electronic devices, however. reliable electrical connections should generally be constructed which do not diminish the beneficial properties of these high-dielectric-constant materials.
Heretofore in this field, single and multiple metal layers are generally used to form electrical contacts to high-dielectric-constant materials. For example, to provide an electrical connection to a high-dielectric-constant material which makes up a capacitor on the surface of a semiconductor substrate, the following structures are among those that have been proposed: (1) substrate/platinum/dielectric, (2) substrate/tantalum/platinum/dielectric, (3) substrate/titanium/platinum/dielectric, and (4) substrate/titanium nitride/platinum/dielectric, where the layering sequence is from the substrate (e.g. silicon) to the HDC layer. Most layering schemes are for high density devices where current flows directly from the bottom electrode to the substrate due to unit area constraints. These layering schemes have the general structure: substrate/oxidizable layer/barrier layer/oxygen stable layer/high-dielectric-constant material. A similar metallization scheme, using the appropriate layers from above, may be used for the top electrode connected to the dielectric film, thus completing the capacitor structure.